The present invention relates to the removal and reclamation of a double metal cyanide catalyst from a polyol formed using the double metal cyanide catalyst.
Preparation of polyether polyols using double metal cyanide (DMC) catalysts is well known. Typically, the DMC catalyst is used in an amount of from 20 ppm to 40 ppm of the polyol product to catalyze the polyol chain formation. When using DMC catalyst at these low levels, however, the reaction parameters must be strictly controlled in order to avoid catalyst deactivation by catalyst poisons introduced into the reaction mixture even in minute amounts, which is difficult in a mass production environment. Further, given the low concentration of the DMC catalyst, the DMC catalyst must also be monitored closely. It is believed that the reaction parameters and process conditions must be maintained in extremely tight ranges when DMC catalyst concentrations are below 100 ppm. Alternatively, it has proven to be desirable to introduce levels of the DMC catalyst to the polyol formation reaction of from 100 ppm to 500 ppm, or higher. At these higher levels of DMC catalyst, however, it is cost prohibitive to not reclaim the DMC catalyst from the resultant polyol. Further, when high levels of DMC catalyst are still present in a polyol when it is used in the formation of polyurethane polymers, the properties desirable in the polyurethane polymer produced can be adversely affected.
When forming a polyethercarbonate polyol from the reaction of an initiator with alkylene oxide monomer and carbon dioxide monomer even higher levels of DMC catalyst, preferably in the range of 100-500 ppm, are required. Because these high levels of DMC catalyst are required, it is imperative to remove the DMC catalyst from the polyethercarbonate polyol prior to its use for the formation of polyurethane polymer. In addition, the DMC catalyst must be recovered from a cost standpoint.
Further, ethylene oxide-capped polyols are difficult to prepare using only a DMC catalyst. Therefore, it is necessary to introduce a second catalyst, such as, for example, KOH, prior to the ethylene oxide addition step after removing or deactivating the DMC catalyst. Therefore, it is desirable to develop a method to rapidly remove the DMC catalyst after the main, DMC catalysed polyol formation reaction step.
U.S. Pat. No. 5,627,120 discloses the preparation of highly active DMC catalysts, which allows the use of the DMC catalysts in low concentrations, eliminating the need for catalyst removal. However, the use of DMC catalysts in very low concentrations leads to the problem of DMC catalyst deactivation by catalyst poisons, which are present in initiators and monomers in minute quantities. It also does not provide a solution to the problem of the production of PO-EO block copolymer polyols, in which case the DMC catalyst has to be removed quantitatively after the PO block is complete.
Various attempts have been made to remove the DMC catalyst from the liquid polyol product in the past. A common form of removal is through cake filtration. One such method is disclosed in U.S. Pat. No. 4,721,818, which teaches reacting the crude polyol with an alkali metal hydride to convert the DMC catalyst into an insoluble species, which can then be removed by filtration. Because, the DMC catalyst particles disposed in the polyol are so fine, an additional filter aid, like diatomaceous earth is usually necessary to form the filter cake upon a filtration media prior to the effective removal of the DMC catalyst from the polyol product. The DMC catalyst cannot be recovered from the filter cake and the filtration process is very time consuming. Additionally, some of the DMC catalyst can remain attached to the polyol polymer chains and therefore, become trapped in the polyol and cannot be removed through filtration.
U.S. Pat. No. 5,416,241 discloses removing the DMC catalyst by treating the DMC containing polyol with alkali metal compounds followed by the addition of magnesium silicate adsorbent and filtration. Again this removal process is designed to convert the DMC catalyst into a filterable form, it is destructive, and the DMC catalyst residue becomes trapped in the resulting filter cake.
U.S. Pat. No. 5,099,075 discloses removing the DMC catalyst by treating the DMC containing polyol with oxidants followed by removal of the residues by filtration, extraction or centrifugation. Again this removal process is designed to convert the DMC catalyst into a filterable form and the active DMC catalyst is destroyed.
DE 1 980 9539 discloses the preparation and use of DMC catalysts on an inert support. The supported DMC catalyst can readily removed by filtration or is retained in the reactor as part of a continuous production process. The problem here is the potential lack of stability of the DMC catalystxe2x80x94support which results in release of the DMC catalyst into the process mixture, contamination of the polyol product with DMC catalyst and loss of catalyst activity.
U.S. Pat. No. 5,248,833 discloses contacting the DMC catalyst containing polyol product with aliphatic alcohols and a chelating agent and removing the insoluble complex formed. The required use of a dilution solvent in combination with the described chelating agents and the required removal of the solvent after removal of the DMC catalyst establishes a complex and expensive process.
Various attempts have been made to separate the DMC catalyst and reuse the separated DMC catalyst.
European Patent EP 385 619 discloses the addition of non-polar solvents to achieve the separation of the DMC catalyst particles form the polyol product. A filter aid is added and the DMC catalyst removed by filtration. The DMC catalyst collected using this procedure may be contained in large amounts of filter aid and no attempts are being made to restore the DMC catalysts original activity.
DE 1 995 7105 discloses separating the DMC catalyst from the polyol product by sedimentation and centrigugation. The addition of large amounts of filter aids is avoided and the DMC catalyst is reused. The separation of the very fine DMC particles by purely mechanical means is technically very difficult, time consuming and costly, however, and the process is not economical.
Although these patents disclose various methods for separating the DMC catalyst from the polyol, they do not disclose a method for solving the problem of recovering an active DMC catalyst from the polyol for reclamation. Each of the prior art methods of separating the DMC catalyst from the polyol set forth above are either destructive to the DMC catalyst or introduce processing steps that render reclamation of the DMC catalyst uneconomical. Therefore, it would be desirable to provide a simple method of removing the DMC catalyst from a polyol while simultaneously solving the problem of recovering the DMC catalyst in an active form and regenerating the DMC catalyst to its original activity by a simple and cost effective process.
The present invention discloses a method of removing and reclaiming a double metal cyanide catalyst used during the formation of a polyol. A reagent that is soluble in the polyol medium is introduced into the liquid polyol product. The reagent is preferably a polymeric acid that is soluble in the liquid polyol. The reagent reacts with the DMC catalyst causing the DMC catalyst and the reagent to form an agglomeration that is insoluble in the liquid polyol product. Further, the reagent extracts DMC catalyst from reaction sites on the polyol chain through protonation of the polymer polyol chain ends to form the agglomeration. The agglomeration forms DMC catalyst particles agglomerates of a large enough size to provide the ability to remove the DMC catalyst from the polyol product by filtration without any filter aids using a standard filter media. In addition the reagent can be separated from the DMC catalyst and the original active DMC catalyst can be regenerated by simple treatment with the original acid contained in the original DMC catalyst.
Through the introduction of a reagent that is capable of reacting with the free DMC catalyst and capable of separating the DMC catalyst remaining attached to the polyol reactive sites, the problems not addressed by the prior art patents set forth above are solved. The inventive reagent forms an agglomeration with the DMC catalyst that increases the effective particle size of the DMC catalyst allowing the DMC catalyst to be easily filtered from the polyol by conventional methods. Accordingly, a conventional filter such as an indexing paper filter may be used to filter the DMC catalyst from the polyol product without having to first form a filter cake of the DMC catalyst. Once the DMC catalyst has been separated from the polyol, the DMC catalyst can be easily reclaimed from the polymeric acid. To be able to efficiently and effectively remove the DMC catalyst from the polyol product and to regenerate the original DMC catalyst allows higher concentrations of the DMC catalyst to be used in the polyol production process. This allows the use of lower quality, less expensive DMC catalyst and reduces the risk of DMC catalyst deactivation by DMC catalyst poisons introduced into the reaction mixture.